46 research outputs found
Ketamine enhances structural plasticity in human dopaminergic neurons: possible relevance for treatment-resistant depression
No full textPluripotent Stem Cell Based Cultures to Study Key Aspects of Human Cerebral Cortex Development
No full textThe human brain is a highly organized structure and the cerebral cortex in particular has expanded massively in size during evolution. The cerebral cortex is arranged into layers of specialized neuron subtypes formed during development by orchestrated stem cell maintenance, expansion, fate commitment and differentiation. The cortical neural stem cells generate billions of neurons in a systematic fashion. The mechanisms and their interplay that control most aspects of human brain development are unclear. This is partially due to the ethical and practical challenges associated with analyzing fetal human development. Recent progress into understanding the formation of the human brain has taken advantage of in vitro modeling of corticogenesis using pluripotent cells. Human pluripotent stem cells and procedures developed for their differentiation provided previously unavailable opportunities to study the mechanisms involved in development of the cerebral cortex. These human cell culture models can be applied to address specific biological questions and have been successfully utilized to investigate mechanisms associated, not only with normal brain
development, but also neuropsychiatric disorders. Here, we review the recent literature that uses these cell culture models to study human corticogenesis. Then, we discuss the challenges and limitations of the current models
Involvement of DA D3 Receptors in Structural Neuroplasticity of Selected Limbic Brain Circuits: Possible Role in Treatment-Resistant Depression
No full textStructural neuroplasticity in the adult brain is a process involving quantitative changes of the number and size of neurons and of their dendritic arborization, axon branching, spines, and synapses. These changes can occur in specific neural circuits as adaptive response to environmental challenges, exposure to stressors, tissue damage or degeneration. Converging studies point to evidence of structural plasticity in circuits operated by glutamate, GABA, dopamine, and serotonin neurotransmitters, in concert with neurotrophic factors such as Brain Derived Neurotrophic Factor (BDNF) or Insulin Growth Factor 1 (IGF1) and a series of modulators that include circulating hormones. Intriguingly, most of these endogenous agents trigger the activation of the PI3K/Akt/mTOR and ERK1/2 intracellular pathways that, in turn, lead to the production of growth-related structural changes, enhancing protein synthesis, metabolic enzyme functions, mitogenesis for energy, and new lipid-bilayer membrane apposition. The dopamine (DA) D3 receptor has been shown to play a specific role by inducing structural plasticity of the DAergic neurons of the nigrostriatal and mesocorticolimbic circuit, where they are expressed in rodents and humans, via activation of the mTORC1 and ERK1/2 pathways. These effects are BDNF-dependent and require the recruitment of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors to allow the structural changes. Since in mood disorders, depression and anhedonia have been proposed to be associated with impaired neuroplasticity and reduced DAergic tone in brain circuits connecting prefrontal cortex, ventral striatum, amygdala, and ventral mesencephalon, activation of D3 receptors could provide a therapeutic benefit. Sustained improvements of mood and anhedonia were observed in subjects with an unsatisfactory response to serotonin uptake inhibitors (SSRI) when treated with D3-preferential D2/D3 agonists such as pramipexole and ropinirole. The recent evidence that downstream mTOR pathway activation in human mesencephalic DA neurons is also produced by ketamine, probably the most effective antidepressant currently used in subjects with treatment-resistant depression, further supports the rationale for a D3 receptor activation in mood disorders
Ketamine increases the expression of GluR1 and GluR2 α-amino-3-hydroxy-5-methy-4-isoxazole propionate receptor subunits in human dopaminergic neurons differentiated from induced pluripotent stem cells
No full textThe mechanisms underlying the prolonged antidepressant effects after a single exposure to ketamine are only partially understood. Converging findings indicate a critical role of structural neuroplasticity, recently also proposed for dopaminergic (DA) neurons known to be involved in a depression core symptom, anhedonia. We recently showed that ketamine induces dendritic outgrowth in human DA neurons differentiated in vitro from iPSC of healthy donors, a phenomenon blocked by the AMPA receptor antagonist NBQX. Since changes of expression of AMPA receptor subunits GluR1 and GluR2 were observed in neuroplasticity of rodent DA neurons, we aimed to explore this phenomenon in human DA neurons. Using specific antibodies against GluR1 and GluR2 AMPA receptor subunits, we demonstrated that GluR1 levels were significantly higher in soma than in dendrites, while for GluR2 levels were significantly higher in dendrites than in soma. One hr exposure to 1 μM ketamine increased the signal of both subunits in dendrites, but only of GluR2 in soma, at 24, 48 and 72 hrs. Non-linear polynomial fitting of dendritic expression indicated that the two curves were significantly different, with a stronger and more sustained effects on GluR2 expression. Both curves showed a relatively rapid building towards higher values when compared with the slow progression of structural plasticity parameters, whose maximal effects were observed at 72 hrs. Overall, these data support a role for GluR1 and GluR2 dendritic upregulation in driving structural plasticity in human DA neurons depending upon ketamine transient exposure, indicating translationally relevant downstream mechanism possibly involved in antidepressant effects
(2 R,6 R)-Hydroxynorketamine promotes dendrite outgrowth in human inducible pluripotent stem cell-derived neurons through AMPA receptor with timing and exposure compatible with ketamine infusion pharmacokinetics in humans
No full textThe mechanisms underlying the prolonged antidepressant effects after a single infusion of ketamine are only partially understood. Ketamine half-life of about 2 hours cannot explain antidepressant effects that last for one week, suggesting the triggering of long lasting neuroplasticity. Recent human pharmacokinetics (PK) data indicate that a ketamine metabolite, (2R,6R)-hydroxynorketamine (HNK), persists in the high submicromolar range for additional 6-12 hours. Since in rodents HNK can induce dendrite outgrowth via AMPA receptor-mediated mechanisms, in this work we aimed to show that HNK produces similar effects in human neurons at concentrations and exposure-time compatible with human PK after ketamine infusion. Human dopaminergic neurons were differentiated in vitro from iPSCs obtained from healthy donors. Exposure to submicromolar HNK for 6 hours produced dendritic outgrowth when measured 3 days after exposure. These neuroplasticity effects were similar to those obtained with exposure to micromolar concentrations of ketamine for 1 or 6 hours and were blocked by pretreatment with the AMPA receptor antagonists NBQX and GYKI 52466, as well as by the mTOR pathway blocker rapamycin. It is reasonable to conclude that the mechanistic similarity of the effects produced by ketamine and HNK and their diachronic brain exposure due to their different plasma PK observed after single therapeutic infusion can contribute to the final sustained antidepressant action
Ketamine effects on mammalian target of rapamycin signaling in the mouse limbic system depend on functional dopamine D3 receptors
No full textKetamine is a noncompetitive glutamate N-methyl-D-aspartic acid receptor antagonist. When acutely administered to rodents, it produces a rapid antidepressant effect. There is evidence that N-methyl-D-aspartic acid receptor blockade enhances glutamatergic transmission preferentially engaging α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors leading to mTOR (mammalian target of rapamycin) pathways activation, thus resulting into downstream neuroadaptive changes in limbic structures. Recent in-vitro data on primary neuronal cultures showed that ketamine activates mTOR also in dopaminergic neurons, and this activation depends on the presence of functional dopamine D3 receptors. The aim of this work was to study the in-vivo relevance of viable D3 receptors in mediating the effects of acute ketamine administration on the mTOR downstream substrate p70 ribosomal S6 kinase (p70S6K), an obligatory substrate for mTOR. We compared the effects of single ketamine 5 mg/kg, 10 mg/kg, or vehicle injection in wild-type and D3 receptor knockout mice. Animals were killed after 60 min, and their brains were processed for p-p70S6K immunohistochemistry. Ketamine increased p70S6K phosphorylation in prefrontal cortex, nucleus accumbens core and shell, ventral tegmental area, substantia nigra, hippocampal CA1, CA2, and CA3, and basolateral amygdala of wild-type mice but not in mutant mice. Our study demonstrates that ketamine-induced p70S6K phosphorylation is dependent on viable D3R expressed in most of limbic structures
Structural Plasticity Induced by Ketamine in Human Dopaminergic Neurons as Mechanism Relevant for Treatment-Resistant Depression
No full textThe mechanisms underlying the antidepressant effects of ketamine in treatment-resistant depression are only partially understood. Reactivation of neural plasticity in prefrontal cortex has been considered critical in mediating the effects of standard antidepressants, but in treatment-resistant depression patients with severe anhedonia, other components of the affected brain circuits, for example, the dopamine system, could be involved. In a recent article in Molecular Psychiatry , we showed that ketamine induces neural plasticity in human and mouse dopaminergic neurons. Human dopaminergic neurons were differentiated from inducible pluripotent stem cells for over 60 days. Mimicking the pharmacokinetic exposures occurring in treatment-resistant depression subjects, cultures were incubated with either ketamine at 0.1 and 1 µM for 1 h or with its active metabolite (2R,6R)-hydroxynorketamine at 0.1 and 0.5 µM for up to 6 h. Three days after dosing, we observed a concentration-dependent increase in dendritic arborization and soma size. These effects were mediated by the activation of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor that triggered the pathways of mammalian target of rapamycin and extracellular signal-regulated kinase via the engagement of brain-derived neurotrophic factor signaling, as previously described in rodent prefrontal cortex. Interestingly, we found that neural plasticity induced by ketamine requires functionally intact dopamine D3 receptors. These data are in keeping with our recent observation that plasticity can be induced in human dopaminergic neurons by the D3 receptor-preferential agonist pramipexole, whose effect as augmentation treatment in treatment-resistant depression has been reported. Overall, the evidence of pharmacologic response in human inducible pluripotent stem cell-derived neurons could provide complementary information to those provided by circuit-based imaging when assessing the potential response to a given augmentation treatment
Structural plasticity in mesencephalic dopaminergic neurons produced by drugs of abuse: critical role of BDNF and dopamine.
No full textMesencephalic dopaminergic neurons were suggested to be a critical physiopathology substrate for addiction disorders. Among neuroadaptive processes to addictive drugs, structural plasticity has attracted attention. While structural plasticity occurs at both pre- and post-synaptic levels in the mesolimbic dopaminergic system, the present review focuses only on dopaminergic neurons. Exposures to addictive drugs determine two opposite structural responses, hypothrophic plasticity produced by opioids and cannabinoids (in particular during the early withdrawal phase) and hypertrophic plasticity, mostly driven by psychostimulants and nicotine. In vitro and in vivo studies indentified BDNF and extracellular dopamine as two critical factors in determining structural plasticity, the two molecules sharing similar intracellular pathways involved in cell soma and dendrite growth, the MEK-ERK1/2 and the PI3K-Akt-mTOR, via preferential activation of TrkB and dopamine D3 receptors, respectively. At present information regarding specific structural changes associated to the various stages of the addiction cycle is incomplete. Encouraging neuroimaging data in humans indirectly support the preclinical evidence of hypotrophic and hypertrophic effects, suggesting a possible differential engagement of dopamine neurons in parallel and partially converging circuits controlling motivation, stress and emotions
Progesterone receptor is constitutively expressed in induced Pluripotent Stem Cells (iPSCs)
No full textSynergic action of L-acetylcarnitine and L-methylfolate in Mouse Models of Stress-Related Disorders and Human iPSC-Derived Dopaminergic Neurons
No full textThe epigenetic agents, L-acetylcarnitine (LAC) and L-methylfolate (MF) are putative candidates as add-on drugs in depression. We evaluated the effect of a combined treatment with LAC and MF in two different paradigms of chronic stress in mice and in human inducible pluripotent stem cells (hiPSCs) differentiated into dopaminergic neurons. Two groups of mice were exposed to chronic unpredictable stress (CUS) for 28 days or chronic restraint stress (CRS) for 21 day, and LAC (30 or 100 mg/kg) and/or MF (0.75 or 3 mg/kg) were administered i.p. once a day for 14 days, starting from the last week of stress. In both stress paradigms, LAC and MF acted synergistically in reducing the immobility time in the forced swim test and enhancing BDNF protein levels in the frontal cortex and hippocampus. In addition, LAC and MF acted synergistically in enhancing type-2 metabotropic glutamate receptor (mGlu2) protein levels in the hippocampus of mice exposed to CRS. Interestingly, CRS mice treated with MF showed an up-regulation of NFκB p65, which is a substrate for LAC-induced acetylation. We could also demonstrate a synergism between LAC and MF in cultured hiPSCs differentiated into dopamine neurons, by measuring dendrite length and number, and area of the cell soma after 3 days of drug exposure. These findings support the combined use of LAC and MF in the treatment of MDD and other stress-related disorders
